The use of rotary immersion vibrators to compact unset material, such as concrete, is well-known in the art. Typically, such vibrators are at least partially immersed into concrete which has been poured into forms to build sidewalks, patios, roads, ramps, bridges, etc., so that the concrete can be vibrated to eliminate air pockets and avoid the formation of undesirable pockets or honeycombs which would decrease the structural strength of the concrete. Normally, a plurality of vibrators are provided, as on a concrete paving machine, with the vibrators, various controls and sensors, paving machine, etc., generally defining a vibration system.
Generally, rotary vibrators include an elongated tubular shaped housing enclosing a rotating eccentric weight which is driven by a motor, normally hydraulic, to generate vibrations. The rotating eccentric weight is normally straddle-mounted by rolling element bearings located at either end of the eccentric weight to transfer the oscillating radial loads from the eccentric weight to the tubular housing.
It is desirable to measure the vibration speed of these rotary vibrators. Optimal vibration speeds can then be determined for achieving maximum structural strength of the concrete which is being vibrated.
Further, the industry is moving toward using drier mixes of concrete to achieve higher structural strength. These drier mixes of concrete require higher vibratory forces in order to be adequately compacted. It is therefore important to monitor the vibration speed of the vibrators to ensure that these high vibratory forces, necessary for the material to be compacted, are being achieved.
Still further, by monitoring vibration speed, the life of a vibrator can be more accurately determined. This would allow a user to take precautionary measures, such as replacing a vibrator that is at or near the end of its "life span", in order to avoid shutdown of a paving machine due to vibrator failure, for example.
Due to the harsh environment in which the vibrator is normally used, it is difficult to design a device for sensing vibration speed which can withstand the normal working conditions of the vibrator. Any external sensing device would have to be capable of withstanding the high vibration speeds which are achieved by the vibrator without becoming detached or disabled. It is generally not feasible to attach a sensing device to the vibrator at an angle generally perpendicular to the axis of the tubular housing, since the sensing device would be prone to breakage. The forces from the concrete or other semi-fluid material would be acting generally transverse to the length of the attached sensing device as the vibrator is being pulled through the concrete, etc., increasing the likelihood of the sensing device breaking off from the vibrator. Also, the external forces acting on the sensing device from the concrete, etc., may affect the operation of the vibration sensing device causing false readings and/or disablement of the sensing device. Further, the sensing device could easily be broken off during transportation of the vibrator.
It is therefore an object of the invention to provide a vibration speed sensor for a rotary vibrator capable of withstanding high vibration speeds normally associated with the vibrator, and also being protected against the harsh environment in which the vibrator normally operates as by being physically incorporated in the vibrator.